This NIDA Center Grant application is for studies of the biomedical aspects of drug abuse with a primary focus on ligand- receptor processes. The central goal is to use the tools of molecular biology and peptide chemistry to study key processes of the opioid systems including their ligands, receptors, and processing enzymes in a coordinated manner to investigate the differential, region-specific and time-related effects of drugs of abuse. The research ultimately will permit the development of human probes for clinical investigation of differential diagnosis, treatment, and prevention. The research is oriented to the mechanisms underlying drug tolerance and ultimately addiction and withdrawal with special emphasis on the endorphins, or opioid peptides, naturally present in nervous tissue which have a key role in drug abuse. The specific goals are to study: 1) opioid precursors in terms of their processing and regulation in order to determine the ways in which the naturally present substances are controlled and how they are affected by drugs of abuse; 2) enzymes which process opioid peptides by cloning them and investigating their normal regulation and how they are altered by drugs of abuse; and 3) the receptors of the opioids by cloning them and investigating their regulation since the receptors may be key to understanding the effects of drugs. As parts of the Center, other drug abuse systems will also be examined. The proposed program expands ongoing studies of members of the Center using the techniques of protein and peptide chemistry (including peptide synthesis, immunoassays, peptide and protein isolation); molecular biology (including cDNA cloning and mRNA techniques); histochemistry (including light and EM immunocytochemistry and in situ hybridization); analytical neurochemistry (including fast atom bombardment mass spectrometry); and human studies in a cross-disciplinary and integrated manner. The more precise understanding of the mechanisms of tolerance, addiction, and withdrawal yielded by the studies and the probes should provide the basis for improving methods of diagnosis, treatment, and prevention of drug abuse.